An area which has received less attention to this point is consideration of the effectiveness of the general ventilation system at controlling chemical concentrations within the laboratory, but outside the immediate area of the hood.8 Traditionally, this ‘‘mesoscale’’ issue is considered primarily at the design stage of new or renovated laboratories, as decisions about equipment placement and ventilation system configuration are made. The primary safety parameter of interest at the mesoscale is the rate at which air contaminants are introduced into, moved through, and then removed from the laboratory; this relates not only to the ventilation rate of the room, but also the size of the room, the layout of furniture and equipment in the room, and the size of the contaminant release.9 Thus, this element is a complicated factor to assess and requires well-informed professional judgment to properly implement. It is only by considering the ventilation system at all three of these scales that the safety value of the ventilation system as a whole for all of its potential receptors can be evaluated. As outlined in Table 2, the elements of the system at the different scales interact in continuously variable ways to form a complex system. We believe that this consideration requires that the laboratory ventilation be managed as a system that includes elements at all three scales on a continuous improvement basis. For this reason, we decided to nest the LVMP defined by ANSI Z9.5 within the management system context described by ANSI Z10.